Positron emission tomography (PET) can detect tumor in vivo based on the living chemistry of cancer tissues. In recent years, PET has well demonstrated its broad clinical utilities in cancer diagnosis and is recognized as an important tool to study cancer functions in vivo, because of its unique ability to elicit molecular functions. The in vivo molecular imaging ability of PET has triggered considerable cancer-research interest and radiotracer development to study cancer related molecular processes such as angiogenesis, apoptosis, cell proliferation, hypoxia, gene expression and blood flow.
Despite this success, the cancer-application potential of PET in whole body is still largely untapped today because of high scanner cost, and low image resolution. As of 2009, clinical PET cameras have imaging resolution of 4.0-6.3 mm, but because of low sensitivity, the practical clinical resolution is worse (7-10 mm), which can miss smaller (early) primary lesions and metastases. In the last decade, researchers have focused on the development of low-cost ultrahigh resolution PET technologies and PET cameras.
PET camera detectors are made up of tens of thousands of scintillation crystals and thousands of photosensors. The most commonly used photosensors in clinical PET cameras are photomultiplier tubes (PMT). Although other solid-state or semiconductor photosensors are also being investigated, such sensors are currently more expensive than PMT.
PET resolution progressively deteriorates from the center due to the depth-of-interaction (DOI) of gamma rays in the thick PET detectors. Secondly, clinical PET image quality suffers from insufficient signal counts. Signal deprivation in PET can typically be alleviated by: (i) increasing the detector depth, (ii) increasing the PET axial field-of-view, and (iii) decreasing the diameter of the PET ring. However, these options cause even worse DOI resolution degradation. The lack of DOI information in clinical PET is due to the high cost of implementing DOI measurements in the large clinical systems. Embodiments disclosed herein include a lower-cost, ultrahigh-resolution DOI PET-detector design, which may provide higher spatial resolution and sensitivity than current commercial PET/MR (PET/CT) systems, while using even less silicon photomultipliers (SiPM) than do the non-DOI PET detectors in current clinical systems. Tens of thousands of costly SiPM and its supporting electronic channels are used to detect the scintillation light from each of the tens of thousands of scintillation-crystal detectors in a PET system. Thus it may enable practical ultrahigh-resolution, high-sensitivity clinical PET/MR and PET/CT with DOI to be realized with a lower production cost than the current clinical PET/MR and PET/CT systems without DOI.